Data is stored on magnetic media such as tape by writing data in a multiplicity of linear tracks. The tracks are separated along the transverse direction of the tape and a given track runs longitudinally along the tape.
In an effort to increase the amount of data that can be written for a given tape width, efforts have been made to make data tracks adjacent to one another. The most common method for writing is to use writers that are spaced apart by a predetermined distance. Furthermore, the predominant method of writing is to have a large separation between readers and a large separation between writers. Adjacent tracks are written in separate passes of the tape where the head is stepped over in the horizontal or transverse direction by the desired track width. The writer width is wider than the desired track width. With each pass, the newly written track overlaps the previously written track so the resulting width of the previous track is the desired final track width. The above described method is termed “shingling”. Another method is to write adjacent tracks simultaneously. As the separation between tracks becomes narrower, horizontal motions of the writing/reading heads relative to the tape will reach values a fraction of the desired read/write track widths.
The technology used in existing tape storage drives aligns the readers within the width of a written track so each reader is aligned over a single track. The reader is typically smaller than the writer, is aligned therewith, and is reading one single track. This method is called “write wide, read narrow.” Because the reader is narrower than the writer, the reader will tend no to read adjacent tracks in spite of the horizontal “wobble” of the tape relative to the reader as the tape moves across the head.
FIG. 1 illustrates a typical multitrack tape head 100 having a multitude of read elements 102 and write elements 104, where the read elements 102 are aligned with the write elements 104. Servo elements 106 (one shown) flank the read elements 102 and are used to sense servo tracks on the medium to keep the head 100 aligned over a data track during reading/writing. The figure shows a “piggy back” structure where a writer is stacked vertically over a paired reader. Many tape heads also have readers and writers which are aligned horizontally, either with groups of readers and groups of writers or alternating readers and writers.
A major drawback to the traditional “shingling” method, however, is that tape wobble increase the probability of overwriting adjacent data tracks during writing the reverse direction and also causes a random variation in the track width along the length of the tape. As the track width decreases, the amount of wobble (or track mis-registration) needs to decrease proportionally. As the track width is decreasing with future generations, it is becoming more difficult to decrease the track mis-registration sufficiently to keep readers on track and avoid overlap of readers on multiple written tracks.
One approach to control the written tracks is to use adjacent writers so a large group of adjacent tracks will be written simultaneously. Any horizontal motion (wobble) during write will cause the simultaneously-written tracks to move together, so the track-to-track separation (pitch) remains fixed within the group. Horizontal motion (wobble) results in large track misregistration during read, as a given reader can straddle two adjacent written tracks.
Furthermore, the servo tracks used for guiding the head-to-tape track alignment are typically written to the tape prior to writing any data. Thus, any wobble of a written track will not be contained in the servo tracks. So, during readback, even though the head is following the servo tracks, errors occur due to the wobble during both writing and readback. The errors can result in a particular reader reading two or more tracks simultaneously, especially where track spacing is minimal. The resultant signal is a composition of two fields from both tracks and may make extraction of the data from any single track impossible.
One approach to solve these problems would be to use a multiplicity of writers and readers, where the number of readers is greater than the number of writers and to allow for the readers to be misaligned with respect to the written tracks so that each reader will have components of more than one track. The data would then be deconvoluted using an algorithm that took the interference into account. A major difficulty in the deconvolution is that the group of written tracks will wobble (or wander) in the horizontal location along the length of the tape.
There is accordingly a clearly-felt need in the art for a head assembly and method for accurately and efficiently deconvoluting a read signal reflecting multiple written data tracks, thereby allowing accurate reading of data in spite of tape wobble. These unresolved problems and deficiencies are clearly felt in the art.